1. Field of the Invention
The present invention relates to a microwave oven, and more particularly to a microwave oven which can uniformly distribute microwaves in vertical and horizontal directions within a cavity, thereby effectively heating foodstuffs.
2. Prior Arts
As is well known, a microwave oven is an appliance for heating foodstuffs by passing microwaves through the foodstuffs. Generally, the microwave oven has a magnetron which generates the microwaves when a high-voltage is applied thereto. In the microwave oven, the magnetron generates the microwaves having a frequency of approximately 2,450 MHz. When the high frequency microwaves are radiated to the foodstuffs contained in a cooking cavity, particles of the foodstuffs are rapidly moved so that a frictional heat is generated from a friction between the particles. The microwave oven heats the foodstuffs by using the frictional heat.
Such microwaves are generated when a high-voltage produced by primary and secondary induction coils of a transformer disposed at a lower wall of a cabinet is applied to the magnetron, and the microwaves are radiated into the cooking cavity through a wave guide.
FIG. 11 shows a conventional microwave oven 400.
As shown in FIG. 11, conventional microwave oven 400 has a cabinet 430. Cabinet 430 includes a cooking cavity 410 and a control chamber 420 which are separated from each other by a partition 415.
A wave guide 450 which guides high frequency microwaves generated from a magnetron 440 into cooking cavity 410 is attached to a predetermined position on partition 415. Magnetron 440 is coupled to a side of wave guide 450. In order to radiate the high frequency microwaves into cooking cavity 410, an aperture 452 is formed at a predetermined position in partition 415. In addition, an antenna 442 for sending the high frequency microwaves is integrally formed at a side of magnetron 440.
A transformer 460 for generating a high voltage is mounted on a lower wall of control chamber 420. Transformer 460 is connected to magnetron 440 so as to apply the high-voltage to magnetron 440.
A cooking tray 480, on which the foodstuffs to be heated are placed, is provided in cooking cavity 410. In order to uniformly heat the foodstuffs, cooking tray 480 is coupled to a shaft 472 of a motor 470, and is rotated while the foodstuffs are being heated.
Microwave oven 400 having the above described structure operates as follows.
Firstly, when a user turns on an operating switch (not shown) attached to a front of cabinet 430, a microcomputer (not shown) installed in microwave oven 400 sends an operating signal to transformer 460. As a result, transformer 460 generates the high voltage and transfers the high voltage to magnetron 440 so that the high frequency microwaves are generated by magnetron 440. The high frequency microwaves are radiated into cooking cavity 410 through antenna 442, wave guide 450, and aperture 452 so the foodstuffs placed on cooking tray 480 are heated.
At the same time, the microcomputer sends an operating signal to motor 470 so as to rotate cooking tray 480 while the foodstuffs are being heated.
However, conventional microwave oven 400 having the above mentioned structure has a disadvantage in that the microwaves are not uniformly distributed in cooking cavity 410, so the microwaves penetrate into the foodstuffs to be heated to a limited depth. For this reason, when a large amount of the foodstuffs are placed on cooking tray 480, the microwaves do not reach a portion of the foodstuffs, so the foodstuffs are not uniformly heated.
In order to solve the above problem, a microwave oven which has a means for stirring the foodstuffs contained in a receptacle, thereby causing all of the foodstuffs to be subjected to the microwaves, has been proposed.
However, the microwave oven requires a sufficient stirring of the foodstuffs in order to uniformly heat the foodstuffs. Moreover, such stirring is difficult when the foodstuffs to be heated are fragile.
On the other hand, U.S. Pat. No. 4,937,418 issued to Boulard discloses a microwave oven which distributes the temperature inside the cooking cavity uniformly while minimizing the stirring of the foodstuffs.
Boulard's microwave oven has a wave spreader including a wave guide. The wave guide has at least one wave-receiving opening formed at an upper portion thereof and at least one wave-diffusing opening formed at a lower portion thereof. First and second deflectors for deflecting microwaves are provided in the wave guide.
However, Boulard's wave spreader is provided as a separate device and installed in the cooking cavity, so the useable volume of the cooking cavity is reduced.
In addition, U.S. Pat. No. 5,698,128 issued to Sakai discloses a microwave oven in which projections are formed in the cooking cavity. In the Sakai's microwave oven, a plurality of convex projections of different sizes are formed in the cooking cavity so as to uniformly distribute the microwaves radiated into the cooking cavity. But, forming the projections in the cooking cavity is difficult and the microwaves are not properly distributed in the cooking cavity if the convex projections are insufficiently provided in the cooking cavity.